There is no federally sanctioned blade length measuring method. In CA and NV it is only the cutting edge that is measured. If you're not sure, go with the conservative estimate and assume that they'll measure from the top of the handle, or "full stabbing depth." I've heard stories of folding knives being measured by the full length of the blade, including the part that's inside the handle when the knife is open, and I heard about a police department somewhere using a fractal computer program to "straighten" out the serrations on a blade to get the length of the blade if it were stretched out, but these are rare and would never hold up in court. I'd say, unless you're in CA or NV, or your state specifically says which method to use, measure from the top of the handle to the tip of the blade.
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Jason aka medusaoblongata
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"I have often laughed at the weaklings who call themselves kind because they have no claws"
- Zarathustra